The present disclosure relates to a coil unit that transmits or receives electric power by electromagnetic induction in a noncontact manner and a noncontact power transmission apparatus having such a coil unit.
In recent years, a noncontact power transmission apparatus is being developed for noncontact charging of electric power into a vehicle such as an electric car, for example. In this noncontact power transmission apparatus, where a power-transmitting coil is provided on the power feed device side and a power-receiving coil on the vehicle side, high transmission efficiency has been achieved by electromagnetic induction in a noncontact manner. Such a noncontact power transmission apparatus using electromagnetic induction has a problem that a leakage electromagnetic field is large because it transmits large electric power, and thus reducing the leakage electromagnetic field is an essential challenge to be addressed. The leakage electromagnetic field includes a leakage magnetic field from a coil and a leakage electromagnetic field caused by a current induced into a conductor such as a metal wound around the coil. Reducing the current induced into the conductor wound around the coil itself is also an essential challenge from a safety standpoint.
Japanese Unexamined Patent Publication No. 2001-148606 describes a technique of reducing disturbance of radio waves by performing balanced driving at both ends of a loop antenna in a wireless communication system.